Cloning Advance, With Question Marks

November 15, 2007|By WILLIAM HATHAWAY; Courant Staff Writer

The disclosure that scientists in Oregon have cloned embryos from monkeys - a close genetic relative of mankind - and harvested precious stem cells comes at a time when scientists themselves are debating the future of cloning.

Results of the work, released Wednesday by the journal Nature, mark the first time a primate embryo has been cloned. The research is an important step in the efforts of scientists to create potentially lifesaving human embryonic cells, which can generate any tissue in the body, from simple skin cells.

"This is one big step toward cloning a human embryo," said Xiangzhong "Jerry" Yang, a cloning pioneer and professor at the University of Connecticut.

However, as scientists at labs in several countries pursue controversial human cloning projects, other researchers are making advances in alternate - and less controversial - ways to create embryonic-like cells.

In the somatic cell nuclear transfer experiment announced Wednesday, the DNA of skin cells was taken from a 9-year-old adult rhesus monkey and fused into a monkey egg that had its own basic genetic material removed. Two of the resulting embryos produced stem cells - valued because they can become every sort of tissue.

Such "patient-specific stem cells" are critical because they are an exact genetic match of the DNA donor. In theory, cells from cloned human embryos could be used without fear of rejection in transplant procedures for a host of diseases and injuries, such as Parkinson's disease and spinal cord injuries.

Scientists also value them because they could be used for research in a variety of hard-to-study diseases, such as dementia and mental illness.

The method has promise, but it also has critics. Opponents of cloning say such work is unethical because early-stage embryos must be destroyed to obtain the stem cells.

And some scientists are also now arguing that it may not be necessary to destroy embryos to obtain such valuable cells. Several labs in the past two years have reported creating embryonic-like cells, in laboratory dishes, that are exact genetic matches of animal donors.

Under a technique called nuclear reprogramming, scientists take skin cells from mice and activate a few dormant genes that are crucial to development of the fetus. The resulting cells appear to be able to do many of the things embryonic cells do - without destroying an embryo.

Yang acknowledges that the technique is very promising, but he also said that many obstacles need to be overcome before reprogramming can create human cells that can be used in therapy.

"The bottom line is that for treatment of human disease, [cloning] is really the closest to creating cures for disease," Yang said.

Although many animal species have been cloned - Yang made headlines in 1999 when he cloned a cow - primates posed so many problems that a few biologists suggested that it might be impossible to clone any primate, including humans.

That view gained support when assertions by a South Korean researcher in 2004 that he had cloned a human embryo proved to be fraudulent.

But the researchers at the Oregon Primate Research Center in Portland, led by Shoukhrat Mitalipov, overcame some of the technical problems in cloning primates by using imaging technology that enabled them to inflict less damage on the monkey egg while removing its nucleus.

Previously, only cloned mice had been used to produce stem cells.

As a result of the South Korean controversy, a second group of scientists reviewed the results of the Oregon group and confirmed that two new lines of stem cells were, indeed, created from skin cells taken from the 9-year-old monkey.

Still, it took more than 300 eggs from 14 monkeys to create the two cell lines. In human terms, that means at least 20 women would have to donate eggs to ensure the creation of a line of embryonic cells, Yang estimated.

Until primate cloning efficiency improves, it will be hard to find women who are willing to donate eggs for research, and human embryo cloning will remain impractical, Yang said. However, he also noted that efficiency in creating embryos has improved dramatically in all animals cloned so far.

Yang, who is on indefinite leave while battling cancer, has suspended his own efforts to clone a human embryo and is helping students to develop animal models of cloning for stem cells. However, other laboratories around the world, including labs in his native China, are continuing the effort.